This invention relates to a manually controllable tuning pulse generator adapted to supply a tuning pulse signal to an electronic tuning control device of an electronic tuning type radio receiver.
Known in the art is a radio receiver which comprises a tuning portion and a tuning control portion comprising a pulse generator capable of generating a count up or count down pulse signal depending upon a manual operation and a clock signal, an up/down counter for counting up or count down the clock signal from the pulse generator depending upon the count up or down pulse signal therefrom and a D-A converter responsive to a count output of the counter for supplying an analog channel selection voltage to varactor diodes included in the tuning portion to thereby operate the latter. The manual pulse generator comprises a disc formed along its periphery thereof with a plurality of slits and capable of being rotated manually and a pair of photo-electric devices each comprising a light emitting element and a light receiving element adapted to receive light from the light emitting element through the slits. The photoelectric devices are arranged in parallel with each other to facilitate the detection of the rotating direction of the disc to determine whether the pulse signal is for up counting or down counting of the clock signal. Such an arrangement is disclosed in copending application Ser. No. 915,098.
The tuning pulse generator constructed as above generates the clock pulse signal having a number of pulses which is proportional to a rotation angle of the disc. The tuning pulse generator of this type is advantageous in that the feeling of the operation of the disc is similar to that of the usual variable capacitor and a fine adjustment of the rotation angle is easy. However, when it is desired to select any one among a number of channels, it is troublesome to do so because a wide range of the disc rotation angle is necessary. In addition to this disadvantage, the pulse generator of this type is disadvantageous in space factor due to the mechanical construction thereof.